1. Field of the Invention
The present invention relates to a computerized tomography system utilizing the nuclear magnetic resonance phenomenon and more particularly to a method and apparatus for magnetic resonance imaging which, in collecting three-dimensional or higher dimensional information by imaging, is capable of shortening the imaging time by effectively performing the process for image reconstruction calculation and enabling the operator to detect in the early stage an abnormality occurring in the course of the imaging due to unexpected movement of the person under inspection or trouble in the apparatus, so that the operability of the apparatus is enhanced.
2. Description of the Prior Art
In magnetic resonance imaging (hereinafter to be referred to as MRI), there have been known methods capable of simultaneously collecting not only two-dimensional tomographic image but also spatial three-dimensional information and further three-dimensional information including chemical shift information or higher dimensional information. As to the method for collecting spatial three-dimensional information, there has been made disclosure, for example, in a literature entitled "Clinical Application of Hexahedron 3-D Fourier Transform" published in Japanese Journal of Magnetic Resonance in Medicine, Vol. 6, Supplement 2, page 120 (September, 1986), or a literature entitled "Study for 3-D FFT Method and Displaying Method" published in Japanese Journal of Magnetic Resonance in Medicine, page 140 (September, 1987). A further example of three-dimensional imaging for spatial two-dimensional information plus chemical shift information, taken as one dimension, is disclosed in a literature entitled "0.1 Tesla SIDAC .sup.1 H-chemical Shift Imaging" published in Japanese Journal of Magnetic Resonance in Medicine, page 104 (March 1987). By combining these methods, it is of course possible to perform imaging to simultaneously collect four-dimensional or higher dimensional information.
A method is also known, imaging a periodically moving portion such as the heart, as to put the apparatus into synchronism with an electrocardiograph or the like and perform a plurality of excitations during each period of a heartbeat and thereby take images at each timing. An example of this method, is discussed in a literature entitled "Time-Resolved Magnetic Resonance Angiography" published in Magnetic Resonance in Medicine, Vol. 6, pp. 275-286, (1988). According to this method, a plurality of N-dimensional images in a time series are obtained and dynamic imaging is made possible.
In the above described prior arts, both the measurement data of the magnetic resonance signals and calculation amount for reconstructing the N-dimensional image from the data become very large. Hence, to reduce the measurement time of the magnetic resonance signals, various methods are proposed as so-called fast imaging methods. However, there has been no consideration given to the problem that it takes time for processing image reconstructing calculation, and hence, a long waiting time is required after the signal measurement has been finished until the image is obtained. Further, when there occurs unexpected abnormality in the course of measurement of signals, such as deterioration in the picture quality due to movement of the person under inspection or trouble in the apparatus itself, the operator expands considerable time before he finds the trouble. As the result, there have been problems of time wasted for repeating the imaging and therefore the operability of the apparatus is diminished.